An absorbent product such as an absorbent pants, a diaper, an incontinence protector, a sanitary napkin, a panty liner or a dressing usually comprises a liquid permeable top layer, a waterproof bottom layer and an absorption body arranged between them.
The top layer is the part of the absorbent product which faces towards the body of the user and the bottom layer is the part of the absorbent product which faces away from the body of the user. The material in the top layer is usually a perforated plastic film, a non-woven or a laminate of a plastic layer and a non-woven layer. The plastic material can be a thermoplastic, such as polyethylene. The non-woven material can be made of natural fibres, such as cellulose or cotton, or synthetic fibres, such as polyethylene, polypropene, polyurethane, nylon or regenerated cellulose.
The purpose of the top layer is an absorbent product of the above type is to lead the liquid into the product, prevent rewetting and in this manner form a dry surface against the skin of the user. A dry surface on the part of the product which lies against the skin of the user is important for comfort and to prevent skin irritation.
The bottom layer is manufactured in a liquid impermeable material. This is to prevent the leakage of liquid from the underside of the absorbent product. The bottom layer can be made of all types of material which fulfill the criterium of liquid impermeability and which have sufficient flexibility for this purpose. Examples of material suitable for the bottom layer are plastic films, non-wovens and laminates of these. The plastic film can, for example, be made of polyethylene, polypropene or polyester. An alternative name for the bottom layer is barrier layer.
The absorption body is usually made from cellulose pulp. It can be supplied in the form of rolls, bales or sheets which are dry defibrated and transferred in fluffed form to a pulp mat, occasionally with the mixing-in of so-called super-absorbent, which are polymers with the ability to absorb many times their own weight of water or body fluid.
The material in the absorption body can, as mentioned before, be cellulose fibres. Examples of other possible fibres are cotton fibres and synthetic fibres.
It is also known to use a foamed material in the absorption body.
Polymer foam with superabsorbent properties for use in absorbent products is described in, among others, EP 0 044 624 and U.S. Pat. No. 4,394,930. Polymer foam without superabsorbent properties for use in absorbent products is described in, among others, EP 0 163 150 and EP 0 229 122.
The problems with absorbent products with three or more layers is that they are expensive and technically difficult to manufacture. The last problem has become more and more apparent as machine speeds have increased during the years. A further problem with multi-layer products is that it is difficult to make three-dimensional body-fitting products. The shaping of the products is limited by the two-dimensional plastic films and non-woven layers which are available.